Question

Force between two identical bar magnets whose centres are $r$ meters apart is $4.8N,$ when their axis are in the same line. If the separation is increased to $2r$ meters, the force between them is reduced to:

• A. 2.4 N
• B. 1.2 N
• C. 0.6 N
• D. 0.3 N

Answer 1

Answer: (D)

0.3 N

$F=\frac{{\mu }_0{m}_1{m}_2}{4\pi d^2}$
$F\propto \frac{1}{d^2}$
$F{d}^2=Constant$
$F_1{d}_1^2=F_2{d}_2^2$
$4.8\times r^2=F_2(2r{)}^2$
$F_2=1.2N$